DS1558

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TYPICAL OPERATING CIRCUIT

DESCRIPTION

The DS1558 is a full function, year 2000-compliant (Y2KC), real-time clock/calendar with an RTC

alarm, watchdog timer, power-on reset, battery monitor, and NV SRAM controller. User access to all

registers within the DS1558 is accomplished with a byte-wide interface as shown in Figure 1. The RTC

registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour BCD

format. Corrections for day of month and leap year are made automatically.

The DS1558 maps the RTC registers into the SRAM address space and constantly monitors A0–A18.

SRAM, and redirects reads and writes to the RTC registers within the DS1558. The DS1558 can be used

with SRAMs up to 524,272 addresses. Smaller SRAMs can be used, provided that the unused upper

The RTC registers are double-buffered into an internal and external set. The user has direct access to the

external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow

the user to access static data. Assuming the internal oscillator is turned on, the internal set of registers is

continuously updated; this occurs regardless of external register settings to guarantee that accurate RTC

information is always maintained.

match user-programmed alarm values. The interrupt is always available while the device is powered from

the system supply, and it can be programmed to occur when in the battery-backed state to serve as a

monitored and an interrupt or reset output are activated if the correct activity is not detected within